Agios Ioannis Rentis, (Greek: Άγιος Ιωάννης Ρέντης, first part meaning Saint John), is a suburb of Piraeus southwest of Athens, Greece. It is located S of Athinon Avenue, about 6 km W of Athens, N of Poseidonos Avenue and NE of Piraeus. The main streets are Kifissou Avenue which is now a superhighway which is also GR-1/E75 for northbound and GR-89 for the southbound lanes and Petrou Ralli Avenue to the north. Also Thivon Avenue runs to the west. The railway line of OSE runs in the southern part.

The area was made up of farmlands and some forests dominated the northern part of the area. The forests are in the squares and used to align with Kifissou Avenue which is now cut down and became a superhighway. In the 1930s and the 1920s, urban development and industrial buildings in the north and east which is part of the Athens Industrial Area replaced much of the farmlands. Today, much of the municipality are industrialized while the urban residential are to the west.

The area is mainly made up of urban areas to the west and the industrial area to the north and the east awas from the Cephissus. A park area with forests lie to the north.